This invention relates to an improved combination weighing method and apparatus providing increased efficiency.
A weighing device, which is generally referred to as a "combination balance" or "combination weighing device", is used for extracting a plurality of articles from a group of articles, such as candies, fruits and vegetables, having relatively large variances in respective weights, to form a sub-group having a weight approximating a predetermined intended weight which will be hereinunder referred to as "reference weight". An example of such a device is disclosed in U.S. Pat. No. 3,939,928 and another example is described in the published British patent specification No. GB2039374A. In these devices, a plurality of articles are weighed individually by a plurality of weighing balances at the same time, all mathematical combinations of the respective weights are summed respectively and the resultant sums are successively compared with a predetermined range of weight for the reference weight. Thus, the combination providing a sum falling within this range is selected for use.
The device also includes automatic loading and unloading means, by which the selected balances are unloaded for collection of the articles thereon into a pack and then loaded with new articles. Upon completion of the loading operation, a cycle of operation of the device is completed and, then, the next cycle is executed similarly. In other words, each cycle of operation of the prior art combination weighing device consists of the steps of combination selection, unloading the selected balances, loading the same balances and, if necessary, transference of the collected articles, and this cycle is repeated periodically.
When the number of weighing balances selected every time is substantially less than the number of remaining ones, a desired combination may be included in the remaining balances. In the prior art device, however, such combination is not taken into consideration until the next cycle of operation is initiated. As the time for combination selection is significantly shorter than the time for unloading and loading, it would be time-saving if the combination selection from the remaining balances could be effected during the unloading step of the preceding cycle and, if a desired combination should be obtained, the corresponding balances could be unloaded after the unloading step or during the loading step of the preceding cycle.
Accordingly, an object of this invention is to provide a combination weighing system which can effect such a partially superposed cycle of operation to increase the device operation.
As well known in the art, the signal level indicative of the measured weight of the weighing balance exhibits characteristic damped vibration after loading and unloading operations and a certain length of time is needed for providing a stable signal level. In the prior art combination weighing system, the time of each cycle of operation is estimated taking this stabilizing time into account and fixedly preset in the device so that each combination selection is initiated after the selected balances have been loaded again and then become stable.
According to a principle of this invention, however, means are provided for inhibiting those balances which are in unstable state to enter into combination, and for effecting combination selection exclusive of these unstable balances and storing a desired combination, if obtained, for the next unloading operation.
These and other objects and features of this invention will be described in more detail hereinunder with reference to the accompanying drawings.